HUDSON RIVER BEDS NEAR ALBANY 495- 



But Hall soon discovered his error in regard to tbis correla- 

 tion with the Point L^vis graptolites and protested against the 

 inclusion of the Hudson river graptolites with those of the slates^ 

 of Point L^vis; as a consequence of which they were omitted from 

 the report of the Canadian survey (decade 2) after having heem 



figured. 



Soon still more facts began to accumulate which threw doubt 

 on that correlation, and finally, in 1877, Hall read a paper (17> 

 before the American association for the advancement of science,, 

 in which the famous investigator fully relates how in joint ex- 

 cursions with his friend. Sir William Logan, along the Hudson 

 river and the adjacent counties, the evidence on which the ori- 

 ginal conclusions were based, was reviewed. He said: 



A farther careful study of the materials collected showed con- 

 clusively that, within the limits indicated, all the fossils were of 

 the second fauna. Many of the species of graptolites, so abun- 

 dant in certain localities of the disturbed and partly altered 

 shales, were also found in the shales and sandstones which gradu- 

 ally assumed an undisturbed and unaltered condition within a few 

 miles west of the river, extending thence through the Mohawk 

 valley, where they rest conformably upon the limestones of the 

 Trenton group. 



With this declaration Hall returned to his former view of the 

 continuity of the graptolite-bearing beds of the Hudson river 

 shales with the Frankfort slates of the Mohawk valley and the 

 Lorraine beds of the northwestern region. It is a misfortune 

 that he does not specify the many species of graptolites which he 

 says are common to the altered shales of the Hudson valley and 

 to the more western undisturbed beds, as this observation forms 

 the principal base of his correlation and has not been verified 

 by other observers, while it disagrees with the writer's result® 

 on the distribution of the Normans kill fauna to the west of the 

 Hudson valley. 



The cause of the misinterpretation of the rocks of the Hudson 

 valley is, in the same address (17:261), very appropriately at- 

 tributed to the "fact, that not only the rocks in the immediate 

 valley of the Hudson, but also those between the river and the 

 eastern limit of the state, were treated as a single group or sya^ 



